It was first part of recrutation task. I had to create simple REST API (almost CRUD, but without update) which would save data to JSON file. I built it on NestJS and deployed on Heroku. It wasn't that easy as I predited, because the Heroku filesystem is ephemeral. I had to save the data.json file somewhere else. I picked AWS S3. So, the API gets requests on Heroku and saves the file on AWS S3. It is deployed.
The second part of recrutation task was a front-end part which should consume the API.